We plan research which will define the initial events which occur during the secretion of extracellular proteins and hormones. Most of the secreted proteins made within cells traverse the membrane barrier of the rough endoplasmic reticulum before being transported within membrane vesicles through and out of the cell. This initial translocation process appears to be mediated through a signal peptide which facilitates binding of the nascent protein to the membrane and is then removed during the translocation process. This "processing" of the signal peptide thus involved proteolytic removal. We will purify and characterize the protease which mediates processing and then examine the fate of the signal peptide.